1. Field of the Invention
The invention relates to a message network for the transmission of digital telegrams with an address consisting of the logical stringing together of routing words, with switching stations, in which in each switching station each incoming line is connected to an input store, for each outgoing line an output store is provided and a routing word associated with it is stored.
Digital message transmission and processing is nowadays widely spread. Thus, there are for example telex networks, digitally-working telex exchanges and message switching equipment for the telex traffic. Moreover, there are digitally-working data transmission networks on telephone lines, which are preferably rented point-to-point lines.
2. Description of the Prior Art
Through German Offenlegungsschrift No. 2,441,099 a combined telephone and telegraph network has become known which is a stage switching system with switching stations connected via digital channels. The messages run, in the form of address-coded message blocks, successively through the switching stages, in which in each stage the selection word which is appropriate for the respective stage and which forms a part of the address is read. The selection word then indicates the outgoing line via which the message block is to leave the switching stage.
The head of the message blocks possesses, inter alia, for the addresses as many selection words as there are switching stages which are to be run through. Thus a selection word having a constant length is associated with each switching stage that is to be run through. Furthermore, the head has one or two control words which act as counters and indicate to the respective address reading device the selection word which has to be read.
The length of the message block heads thus fluctuates according to the number of switching stages which the respective message block has to run through, but remains constant for the entire life of the block.
The head of the message blocks is thus relatively rigid and is predominantly suitable when a lot of information is to be transmitted at the same time. For short message blocks, the head would be too long and the ratio of useful information to head length would become very unfavorable.
Upon applications for telephony, each 8-bit information word incorporates a PCM scanning value, so that with at the most 256 8-bit control and information words for a single message block a considerable number of scanning values is simultaneously transmitted. This causes, in the end apparatus, a considerable expenditure for the preparation or the processing of the message packets, which respectively have to be stored as a whole. Through the input, output and intermediate stores in the switching stages, the expenditure for the stores which are necessary in the telephony and telegraphy network formed is multiplied.
German Offenlegungsschrift No. 2,441,099 thus described substantially a storage switching network for telegraphy and telexing which, through particularly rapid switching stages and special priority signals in the message block heads can also be used for telephony applications.